Method of freezing an earth formation



y 13, 1965 c. E. SCHROEDER 3,183,675

METHOD OF FREEZING AN EARTH FORMATION Filed Nov. 2, 1961 FIG. 1

INVENTOR. Carl E Schroeder BY M 6/ United States Patent 3,183,675 METHODOF FREEZING AN EARTH FORMATION Carl E. Schroeder, Ponca City, Okla,assignor to Conch International Methane Limited, Nassau, Bahamas, a

The invention relates to a method of freezing an earth formationcontaining or impregnated with a liquid by inserting cooling tubesvertically into the earth formation and passing a refrigerant throughsaid cooling tubes.

The invention relates in particular to such a method for use in thepreparation of a reservoir for the storage of liquefied gases whichcomprises a hole in the surface of the earth.

In this specification the expression liquefied gas, means liquid whichboils at atmospheric pressure at a temperature below the ambienttemperature and the expression a hole in the surface of the earth meansa place in the surface of the earth which has a substantial area on theplane of the surface in relation to its capacity.

Liquefied gas can be stored successfully in a hole in the surface of theearth, provided that the earth formation surrounding said hole is sealedby a liquid which is in frozen condition at the boiling point of theliquefied gas to be stored. Preferably the hole is completely covered bya heat-insulated roof so as to diminish the influx of ambient heat tothe liquefied gas stored in the hole. A reservoir of this kind isdisclosed in U. S. Patent No 3,159,006.

The hole may be a naturally occurring one or it may be made artificiallyby excavation or by suitable explosion forces. When working in a verywet earth formation it may be desirable to freeze the water in the earthbefore carrying out the excavation. When working in dry sand it may bedesirable to impregnate the area in which the hole is to be made withwater, then freeze the water and carry out the excavation. In the casethat the earth formation is not very wet it is possible to make the holefirst by excavation and to freeze the water in the earth formationsurrounding the hole afterwards but before storing the liquefied gas inthe hole. In all cases the earth formation can be frozen by means ofcooling tubes inserted vertically into the earth and by passing arefrigerant through said cooling tubes.

Now in the method according to the invention, the cooling tubes used areof a kind having an outer surface which is provided with a continuoushelical fin.

The continuous helical fins assist in the installation of the coolingtubes in the earth formation and they provide a better heat transferbetween the cooling tube and the earth formation. Furthermore, thehelical fins provide a good anchorage of the cooling tubes in the earthformation. Also the continuous helical fins make it possible to fill upcompletely with earth the spaces between the fins.

The invention will now be further explained with reference to thedrawings, in which FIG. 1 shows a cross section of an earth formation inwhich the cooling tubes according to the invention are present;

FIG. 2 shows a plain view of the arrangement according to FIG. 1; and

FIG. 3 shows in detail a cooling tube having a continuous helical fin.

The cooling tubes 1 are provided with a continuous helical fin 2. Eachcooling tube 1 is also provided with an inner tube 6, an inlet 3 and anoutlet 4. The earth formation is indicated by the numeral 5. The hole tobe excavated in the earth formation 5 is indicated by the dotted line 7.

Each cooling tube 1 can be inserted into the earth formation 5 byrotating it around its vertical axis and by exerting a downward force onit. Preferably a hole 8 is first made in the earth formation and thenthe cooling tube is inserted in the hole 8. The hole 8 has about adiameter corresponding to the outer diameter of the continuous helicalfin 2. The spaces between the windings of the helical fin 2 can befilled up with earth or sand 5a after installation by rotating thecooling tube 1 around its longitudinal axis. When the cooling tubes 1have been inserted into the earth formation a refrigerant is introducedinto each inlet 3 of each cooling tube 1 by means of suitable piping(not shown in drawings) which is then attached to inlet 3. Therefrigerant passes downwardly through the space between inner tube 6 andthe outer wall of each cooling tube 1 and then upwardly through theinner tube 6. Finally the refrigerant flows out of outlet 4. By means ofsuitable piping, which is attached to outlet 4 after the cooling tubesare installed, the refrigerant is then led to a cooling installation forcooling the refrigerant down again. After passing the coolinginstallation the refrigerant is again led by means of suitable piping tothe inlet 3 of each cooling tube 1. By passing the refrigerant throughthe cooling tubes 1, the liquid (in most cases water) contained in theearth formation 5 will freeze.

When it is intended to construct a hole in the ground for storingliquefied gases, the cooling tubes 1 are inserted into the earthformation 5 in a roughly circular manner. Then refrigerant is passedthrough the cooling tubes 1 so that the earth formation is frozen andthen a hole 7 is excavated in the frozezn earth formation 5. Finally aheat insulated roof is placed over the hole in the ground. Instead ofexcavating the hole 7 after freezing the earth formation 5, it is alsopossible, however, to excavate the hole 7 first and to freeze the earthformation 5 after excavating the hole 7. If the earth formation is verywet, however, the first mentioned method is preferred.

I claim:

1. Method of freezing a moist earth formation comprising the followingsteps:

(a) excavating a cylindrical hole in the surface of the earth;

(b) inserting into said hole a cooling tube having a helicalheat-conducting fin fixed to the outer surface of the tube, said finwinding around said tube along the length from the inserted end thereofand having a slightly lesser outer diameter than said hole, said tubebeing positioned with its other end projecting from said hole;

(c) back-filling the space between the wall of said hole and the outerwall of said tube with loose waterpermeable backfill material by addingsaid backfill material at the top of the hole and rotating said tube ina direction such that the spaces between the windings of the helical finare filled by the backfill material;

(d) circulating a refrigerant through said cooling tube to freeze themoist earth in the vicinity of the tube.

2. The method according to claim 1, said cooling tube having an innerconduit and an outer conduit surrounding said inner conduit andinterconnected with said inner conduit at the bottom of the tube,including the step of passing said refrigerant from the top of the tubedown trough one of said conduits and up through the other conduit backto the surface of the earth.

(References on following page) 3 4% References Cited by the Examiner2,932,170 4/60 Patterson et a1.

UNITED STATES PATENTS 2,961,840 11/60 GO'ldtl'flP 62-45 OTHER REFERENCESX 5 Engineering News-Record, paggsr 74-76, May 11, 1939. ggfii l 61 36EARL J. WITMER, Primary Examiner.

Meade et a1 6136 X WILLIAM I. MUSHAKE, Examiner.

1. METHOD OF FREEZING A MOIST EARTH FORMATION COMPRISING THE FOLLOWINGSTEPS: (A) EXCAVATING A CYLINDRICAL HOLE IN THE SURFACE OF THE EARTH;(B) INSERTING INTO SAID HOLE A COOLING TUBE HAVING A HELICALHEAT-CONDUCTING FIN FIXED TO THE OUTER SURFACE OF THE TUBE, SAID FINWINDING AROUND SAID TUBE ALONG THE LENGTH FROM THE INSERTED END THEREOFAND HAVING A SLIGHTLY LESSER OUTER DIAMETER THAN SAID HOLE, SAID TUBEBEING POSITIONED WITH ITS OTHER END PROJECTING FROM SAID HOLE; (C)BACKFILLING THE SPACE BETWEEN THE WALL OF SAID HOLE AND THE OUTER WALLOF SAID TUBE WITH LOOSE WATERPERMEABLE BACKFILL MATERIAL BY ADDING SAIDBACKFILL MATERIAL AT THE TOP OF THE HOLE AND ROTATING SAID TUBE IN ADIRECTION SUCH THAT THE SPACES BETWEEN THE WINDINGS OF THE HELICAL FINARE FILLED BY THE BACKFILL MATERIAL; (D) CIRCULATING A REFRIGERANTTHROUGH SAID COOLING TUBE TO FREEZE THE MOIST EARTH IN THE VICINITY OFTHE TUBE.